I suspect you mean the Content Library pane and not the Render Library pane, since the former can be used to "load a certain item into the scene" and the latter cannot. Both panes are provided with the standard distribution, but both are [separate] plugins. Plugins (compiled C++ that make use of the libraries/headers provided with the SDK) are not generally accessible by other plugins… unless they have been built, explicitly, for that purpose; most are not. However, both panes are accessible via script - I answered a similar question in more detail, in the Developer Discussion forum, here. In my response, you'll notice references to a Content Manager (i.e. "oContentMgr"). This is the class ("DzContentMgr"), accessible by script and by plugin, that is used to load user-facing files.